The present Applicant's prior French patent FR No. 2 545 129 describes a prefabricated block of the type mentioned which is constituted by a slab of cement (or of any other similar hardenable binder), with one of its faces being lined with visible juxtaposed stones which are held fast by the cement. Two opposite edges of the slab are in the form of irregular lines (e.g. zig-zag lines) suitable for mutual interfitting. This arrangement serves to mask the joints between two adjacent blocks when assembled together, in particular when erecting a wall or laying a paving, and the assembly obtained in this way imitates a continuous pile of dry stones.
At present, in order to manufacture an block of this nature, the Applicant begins by placing the stones, e.g. rejects from granite cutting, side-by-side on the bottom of a mold having an open top and having sides which are identical in shape with the shape of the block to be manufactured. A metal frame may optionally be placed over the layer of stones in order to improve the mechanical strength of the finished block and then fluid cement is cast into the mold. Once the cement has set, the finished block is removed from the mold.
Experience has shown that this traditional method used by the Applicant does not give full satisfaction since the cement does not always completely and fully fill the mold, thereby giving rise to voids which are unacceptable on grounds of the block's appearance or its mechanical strength, and which sometimes give rise to the stones being poorly retained by the cement. In addition, the cast cement frequently reaches the visible portions of the stones and sets on said portions, thereby spoiling the appearance of the finished article.
The invention seeks to mitigate these problems by proposing a manufacturing method of the type mentioned which is easy and cheap to implement, which enables very high quality finished blocks to be obtained with a low reject rate, and which is suitable for medium to large scale production.